Gaseous discharge device



March 1, 1960 T. A. VANDERSLICE 2,927,240

GASEOUS DISCHARGE DEVICE Filed Sept. 25, 1958 Fig. 3

/nvenforz Thomas A l/anders//ce f M 6 4% H/'s Afforney.

United States Patent-O 1 2,927,240 GASEOUS DISCHARGE DEVICE Thomas A. Vanderslice, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Application September 25, 1958, Serial No. 763,292 7 Claims. (Cl. 313-193) The present invention relates to improved gaseous Vdischarge devices and, more particularly, to improved anode structures therefor.

In gaseous rectier devices, such as thyratrons and the like, one serious cause of tube failure after a substantial period of operation is the occurrence of gaseous cleanup whereby the gas pressure within the device gradually drops to a value at which a gaseous discharge may not be sustained between the anode and cathode thereof.

A further disadvantageous aspect of the clean-up phenomenon is the fact that, as pressure decreases, the operating parameters of the device, for example, breakdown potential and operating potential difference, are subject to change. This change may render the device useless as a control or regulatory device long before actual failure occurs.

Accordingly, one object of the present invention is to provide gaseous discharge devices having improved and longer lifetime characteristics.

Another object of the present invention is to provide gaseous discharge devices which are capable of maintaining a constant operating pressure over an extended period of time.

Still another object of the present invention is to provide improved anode structures for gaseous discharge devices.

Briey stated, in accord with one feature of my invention, l provide an improved long-lifetime gaseous discharge device suitable for use as a rectifier or regulator of alternating electric currents and including a cathode and a closely-disposed hollow anode wherein the aperture into the anode cavity is smaller than the inside dimensions of the anode cavity. 1n accord with another feature of the invention, a control electrode is disposed between anode and cathode to form a triode gaseous discharge device of the thyratron type. The anode structure utilized insures substantially uniform current density over the anode surface utilized, and the hollow, partiallyforeclosed anode surface facilitates control and confinement of metallic particles sputtered from the anode by positive ion bombardment during the inverse alternation of an applied alternating voltage sought to be regulated or rectified.

The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the attached drawing in which: Y

Fig. 1 illustrates a gaseous three-electrode discharge device constructed in accord with one feature of the present invention,

Fig. 2 represents an alternative embodiment of the invention utilizing the disc-seal construction for gaseous discharge devices,

Fig. 3 represents a two-electrode gaseous discharge device constructed in accordance with another feature of the present invention, and

Fig. 4 represents an alternative electrode structure which may be utilized in any of the embodiments of Figs, 1, 2 and 3.

In Fig. 1, a triode gaseous rectifier or control device of, for example, the thyratron type, constructed in accord with the present invention includes an evacuable vitreous envelope which may, for example, be of Pyrex glass having rez-entrantV portions and 3 at opposite ends upon the anode and portions of the anode which are 2,927,240 Patented Mar. 1, 1960 ICC thereof. An electron emissive cathode 4 is supported from re-entrant portion 2 by cathode lead 5 and cathode support 6. A cathode heater 7 may be supplied and, if present, is utilized to heat cathode 4 to thermionic emission temperatures by virtue of its location within the cup of cathode 4. v Heater 7 is supported by and electrically connected to a suitable filament supply by support and lead-in wires 8 which pass through re-entrant portion 2 of envelope 1. A hollow anode 9 is composed of a hollow metallic shell in the form of a hollow oblate spheroidal body, truncated along a line substantially perpendicular to the polar axis thereof to form aperture 10. The interior of anode 9 defines anode cavity 12. A control grid or electrode 11 is interposed between cathode 4 and hollow anode 9 and serves to control the passage of electric current therebetween. The interior of envelope 1 is filled with a noble gas as, for example argon, at a pressure of the order of 5-10 microns of mercury. Cathode electrode 4 is composed (if thermionically operated) of a low-work function material as, for example tungsten or thoriated tungsten. The interior surface 13 of anode 9 bordering upon anode cavity 12 is the active anode surface and is conveniently formed of a material which is diflicultly sputtered under positive ion bombardment such as niobium or tungsten. The exterior of anode shell 9 is conveniently, but not necessarily coated with a non-conducting layer 14 to prevent the footpoint of a glow discharge being established upon the anode exterior rather upon the interior thereof. An alternating voltage to be rectied is connected across anode and cathode electrodes. Current ows therebetween when the anode is suiciently positive to overcome the negative bias of control electrode 11.

In the operation of devices similar to that illustrated in Fig. 1, but possessing a conventional planar or cupped shaped anode, tube life and tube reliability and stability have, heretofore, been seriously affected by a constant and progressive lowering of the pressure of the inert gases with which the device is charged. l have determined that this lowering of gas pressure or gas clean-up is the result of the formation, upon the interior walls of the tube envelope, of a thin layer of metal which is sputtered from the anode electrode by positive ion bombardment during the inverse cycle of an alternating voltage across which device is connected and which the device is utilized to control or rectify. Thus, in operation, a glow discharge is established betweencathode and the anode when the positive potential applied to the anode is sufcient to overcome the negative field established by a potential applied to the control electrode. The glow discharge continues as long as the anode remains positive with respect to the cathode. When, however, the alternating voltage applied between cathode and anode reverses polarity and the anode becomes negative, a glow discharge is not reinitiated because substantial cold emission does not occur from the anode. At that time, however, there are alarge number of ionized gas molecules present in the space between the anode and cathode. These positive inert gas ions are then accelerated into the anode and strike the anode `with energies sufficient to cause the ejection of particles of anode material therefrom. These particles migrate to the tube walls where they form a sink for the deposition of positive gas ions which are subsequently covered up by further sputtered metallic particles. Thus, over a long period of time a number of gaseous ions are collected in materials sputtered to the tube walls from theV anode Iand the gas pressure falls, eventually causing tube failure. p Y v' t A further disadvantage, in triode devices as, for ex ample those illustrated in Fig. 1 of the drawing, is that, a planar anode, the control electrode casts a shadow is gained through aperture "24, and defining ananode discharge devices, an annular ange portion` 26' conn 'ted with cathode 20 mechanically supportsrcatho'd'e' Zllaid' facilitates electrical contact thereto. Likewise, an an- Y nular ring 27- is connected with, and supports, control acetate Y shielded `fronitlic cathode by a closely spaced control tered metallic particles which are removed fromy therremaining portions of the-anode by positive ion bombardment. These portions of the anode likewiseV serve as a 'sink for the reception of gas ionsV and the entrapment thereof by sputtered metal. f Thisphenomenon also contributes to the cleaning up of gas withinthe tubesde creasing of gas pressure, in the eventual failure of the tube; Y

The device of Fig. l, on the' other hand, pr'everitsthe foregoing cleaning up actions by virtue of two separate but interrelated characteristics of anode.KV Initially, it

has lbeen found that the non-planar anodesurface 13 results in a substantially uniform current densityover all Vportions thereof irrespective ofthe presence-of control electrode 11. This completely eliminates, from triodeY devices any effect of grid shadow which causes the creation-of small gasrion sinks on the anode surface itself.

Additionally, and of greater importance', is-the fact that the restricted entrance of orifice 11 into anode cavity 12 very greatly reduces the probability Vthat metallic particles sputtered from one portion of the interior surface 1'3. of anode 9 will possibly beV able to migrateto Athe interior of envelope 1 to cause the formation of 'a sink 'for gaseous ions which may later'be covered up andrem'ovedvfrom the device by subsequently sputteredl metallicparticles, lowering the pressure thereof. In thea'node configuration utilized in the device of Fig.' l and' in equivalent anode structures, most anodematerial sputtered from the interior surface 131of hollow anode 9 by positive'ionY bombardment during the inversecycle of an applied alter'- natingvoltage is collected at another portionof the anode surface due to the factv that the 'solid angle 'subt'eded from any given spot on the anode surface 13by orifice' l11 is a relatively small fractionV of the total solid angle. In the operation of the device' of Fig. l, any metallic par'- ticles sputtered from the interior surface 1'3 of anode 9 generally are collected by another portion!v of the sante surface and very'little' of the anode material is allowedto' escape from the interior of'anode cavity 12.Y No ga cous ionsrareY entrapped at the anode because these de'ros'itedv 'metallic particles are V'continuously relsputteifedf The Y' clean-up of inert gas lis therefore substantially `vpre- Vvented and the gaspres'sure withinv the discharge device remains 'substantially constant over` the entire Vtube life-V yyhich isY determined, then, by factors other than by gas clean-up.l In this embodiment of the` invention 'gas Yclean-up is; further prevented by the utilization"`o f Va dicult'ly Vsputtered material,l suchas nobin'i 'oi-tungsten the interior surface 13 of. anode electrode-9; In Flg. 2 of the drawing there is illustrated Y Y In Fig. 2, cathode zo, donn-01 .electrode zr and anode block zzp-having a truncated oblate s'pher'olidalA'acti` anode surface' Z3 onthe interior thereof, acces'sto' i electrodeZil. The' outside diameterof both of these members islsubstantially the's'am'e'as thefeite'ior diani-v eter of anode'y blockV 22. Thisfaeilit'ates the" assemblyi'of *.65 .cavity 25 are analogous to' cathode, control electrode andV` anode ofthe device of Fig. l. Additionallas is con-V sxstentwith' thedisc-seal technique offabricatingel c the `device -in conventional disc-seal fashion whereby alternate metallic members 22, 26 and 27 Vare separated by ceramic members ofV a like enterior dimension to form an hermetically ysealedenvelope; To complete the structure, a heater 'filament 2'8 may be enclosed within the cup of 'cathode 20. Onev end ofheater lament-28- is connected to metallic end mrnber'29 and the otherlead is connected to cathode 24).y To ":om`ple`tev theevacuable Venvelope of thek dischargedevice Villustrated in Fig. 2, anode 22 is electrically insulated from, and hermetically sealed to,l control Velectrode support 4member 27 by` a suitably counterbored and recessed ceramic member 30. Member 27 -is electrically insulated from, and hermeticallysealed to, annular memberZ by a suitable annular ceramic member i311,V properly counterbored and recessed, Member 29 is likewise' electrically insulated from', but hermetically sealedto, member'Zj by annular member3-2. y Y g g if Thexdevice of'FigAZ- may. be 'assembledand sealed inY aninertatmosphere-'byt theprocess disclosedY and claimed in the depending.'application Yof.V James M. Laierty, 690,849, ledOct. Y17, 1957,and .a'ssigned to the same assignee'. as' lthe present invention. The operating characteristics ofthe device `of Figf. 2 are identical with those of the devices of Fi'g.f1 andthe advantages gained therefomover triode rectifier orrgulatin'g devices is identical thereto, the main difference being that this device incorporates onlymetallic and ceramic membersl and hasA all the advantages ofV ceramic and m'etaldiskfseal discharge devices. o y

lnvFig; 3 of .the drawingthere is illustrated a twoelement gaseous electric discharge device constructed in accord with the presentinvention. The' device of Fig'. 3 maybe a Vvoltage regulator or voltage reference' tube utilized to maintain a constant voltageacross anetwork or` alternatively may be aV simple rectifier device utilized torectify an alternating voltage. y Y The device'of Figi. 3 'is similar to that of Fig. 2 but is a two electrode device, including a cathode 35 and an anode 36'hav`ing`an anode cavity 37 therein and an active auodesuface'. Cathode 35 'is supported by annular member 39 which is electrically insulated from, but hermeticallysealed to, anode block 36 by'a properly counter-Y bored: andv groot/eid annular insulating member 4Q. Cathode' 335 may be raised to thermioiiic emission temperatures by a heater lam'efnt`-41, one e'rid of which is connected to' 'cathode' 35, and the other end ofwhich is connected to ed niembe 42 which isY electrically insulated from and hern'ie'tically sealed-to, annularcathode support 39 by means ofannular ceraniicy member 43.

ln the operation of the device of Fig. V3 the space between the cathode and anode surface is lled with a suitable noble gas as, forY example argon, Vat a suitable pressure s,for example, Afrom S-'lO microns of mercury pres-v sure and, whenanodeV surface 38 is maintained positive with-respect to cathode 35, a "glovsdischargeV initiated therebetween. Whilel the dischargeaexistsy between anode and cathode, the voltage diferenceftlierebetweeiis imple, sv vous. wim,

age occurs, and anode 38 becomes negative to cathodelSS, nodiscliarge enists and the line voltage applied between anode and cathode. This causes ionized these' Ametallic particles are, a high probability, re-

deposited 'upon other portions of anode'surface `38 bef cause of ther-small aperture inthe hollowanode block 36 as,compared withfthe entireA area of anodei'surface 38.,

Thispreveiits theaccumlrllationof sputter'ed anode mai te'nralguponfthe interior wallslofthedevice which would merida asiel# fcr the @climtica Of'sble Se isis and a resintant lowering'the Ygaseous pressure'with the device. Additionally, .the hollow anode, with a restricted entrance thereto reduces to a low value the probability that ionized gaseous molecules will migrate to thecold walls of the tube and possibly damage the ceramic or glass-tometal seals. This advantage exists in all embodiments of the invention.

In Fig. 4 of the invention there lis shown, schematically, an alternative anode structure which may be applied to any of the embodiments of the invention illustrated in Figs. 1, 2 and 3. In Fig. 4 the anode structure, rather than being an oblate spheroid, as are the anode cavities in the devices of Figs. l, 2 and 3 is, rather, a hollow cylindrical body 44 with an inwardly depending flange or cap at the end thereof. Although Athis structure does not have the ideal characteristics of the anodes illustrated in Figs. 1, 2 and 3 it may be fabricated with greater ease and, therefore, is less expensive and more easily manufactured. The anode of the Fig. 4 may readily comprise a metallic disc 45 to which there is connected an annular member 46 which is capped with annulus 47, all connections `'being made by spot welding, brazing, soldering or other well known techniques. The material from which anode 44 of Fig. 4 is constructed may be any suitable material as mentioned hereinbefore which is diiiicult to sputter under positive ion bombardment. in all embodiments of the invention it is desirable that the ratio of aperture diameter to anode cavity diameter be 1/z or less to secure the full beneiits of the invention.

lt should be noted that the present invention is related only to gaseous discharge tubes wherein a finite amount of a gas such as the inert and noble gases, for example, nitrogen, helium, neon, argon, krypton, Xenon and radon are utilized as the sole ionizable medium for the conduction of electric current between the cathode and anode thereof. This invention is based upon my discovery of the mechanism of gas clean-up in such tubes and therefore is entirely unrelated to other types of discharge devices, such as tubes operating in vacuo, wherein a finite gas pressure is not necessary, or pool-type discharge devices, such as mercury vapor tubes of the thyratron or an ignitron type, wherein a continuous vapor replenishing reservoir is provided as, -for example, by a pool of mercury in the vicinity of the cathode. Obviously, since there is a continuously replenishable supply of mercury vapor in such devices, a provision of an anode such as is disclosed in the present application would have little or no added advantage.

While the invention has set forth hereinbefore with respect to certain embodiments thereof, many modifications and changes will immediately occur to those Skilled in the art. Accordingly, by the appended claims I intend to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and a hollow anode electrode having an aperture therein, the largest dimension of said aperture being less than the interior dimension of said hollow anode by a factor of no greater than 1/2 measured in a plane substantially parallel with the plane dened by said aperture, said cathode and said anode being closely juxtaposed so as to sustain a glow discharge therebetween; and a pressure of gas suficient to sustain a discharge constituting ionized gas particles within said envelope.

2. A gaseous electric discharge device comprising an evacuable envelope containing therein a cathode and an anode electrode each of which has an active surface adapted to serve as the terminal point of an ionized gaseous discharge, said anode surface `being the surface of a partially enclosed cavity the entrance aperture of which is in a plane substantially parallel to the plane of the active surface of said cathode and which is smaller in dimension than the dimension of said cavity by a factor no greater than l/ measured substantially parallel with the plane of said aperture, and a pressure of gas sufiicient to sustain a discharge constituting ionized gas particles within said envelope.

3. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and a hollow anode electrode, the active surface of which is the interior surface of a truncated curved cavity within said anode, said cavity being terminated in an aperture in a plane substantially parallel with the active surface of said cathode, the dimension of said aperture being less than the dimension of said cavity substantially parallel with said plane; and a pressure of gas sufiicient to sustain a discharge constituting ionized gas particles within said envelope.

4. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and an anode electrode closely disposed to one ano-ther and having active surfaces adapted to form the terminal points of a gaseous electric discharge, said active anode surface being the interior of a hollow cylindrical body having a completely closed end at a point remote from said cathode and an inwardly depending annular flanged end at a point closely disposed to said cathode, the interior dimension of said flanged member being no greater than lo the interior diameter of said cylindrical body; and a pressure of gas suiiicient to sustain a discharge constituting ionized gas particles within said envelope.

5. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and an anode electrode closely disposed to one another and having active surfaces adapted to form the terminal points of a gaseous electric discharge, said anode surface being the inner surface of a truncated oblate spheroidal cavity in said anode, the entrance aperture to said cavity having a diameter substantially parallel to said cathode emissive surface which is less than the diameter of the spheroidal cavity substantially parallel therewith; and a pressure of a gas suiiicient to sustain a discharge constituting ionized gas particles within said envelope.

6. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and an anode electrode closely disposed to one another and having active surfaces adapted to form the terminal point of a gaseous electric discharge, said active anode surface being the interior of a hollow cylindrical body having a completely closed end at a point remote from said cathode and an inwardly depending annular flanged end at a point closely disposed to said cathode, the interior dimension of said tianged member being no greater than 1/z the interior diameter of said cylindrical body; a control electrode interposed between said cathode and said anode and a pressure of gas suicient to sustain a discharge constituting -ionized gas particles within said envelope.

7. A gaseous electric discharge device comprising an evacuable envelope having therein a cathode electrode and an anode electrode, closely disposed to one another and having active surfaces adapted to form the terminal points of a gaseous electric discharge, said active anode surface being the inner surface of a truncated oblate spheroidal cavity in said anode, the entrance aperture to said cavity having a diameter substantially parallel to said cathode active surface which is less than the diameter of the spheroidal cavity substantially parallel therewith; a control electrode interposed between said cathode and said anode and a pressure of gas sufficient to sustain a discharge constituting ionized gas particles within said envelope.

References Cited in the le of this patent UNITED STATES PATENTS 

